The present invention is directed towards a geothermal cell and recovery system.
The most common source of heating or cooling is the surrounding air because of its accessibility. However, since the air is heated to high temperatures in the summer and cold temperatures in the winter, it is the least efficient source of cooling and heating. The use of water as a heat source is more efficient than atmospheric air. However, the impurity, quality, quantity and disposal of water and the corrosion problems of pipes handling the water have minimized the use of such systems.
It has been established since at least the early 1900's that earth (be it soil, clay or stone) was a good insulator. This made it possible to store ice for long periods of time in pits as it is known that the temperature of the earth remains rather constant at as shallow a depth as 36 inches or in colder regions under the frost line.
There have been numerous attempts to recover or utilize heat from the earth. Some of the earlier recovery attempts used large numbers of refrigerant lines buried beneath the surface of the earth. Others developments required the drilling of numerous, and sometimes deep, water wells to develop a sufficient water supply. Still other developments used a brine solution with piping buried beneath the soil. These earlier attempts have major drawbacks which have prevented their success and curtailed development. Modern day home owners do not have sufficient land needed to bury a piping array underground and are precluded from such installation by zoning ordinances. Other home owners lack the certainty of hitting water of sufficient quantity to afford drilling a well or wells. Furthermore using a brine solution which is circulated in large piping arrays underground is undesirable because of the environmental problems which include potential possibility of contamination of the sub-soil and ground water and the large building lot size required. The prior art devices used were not as intrinsically safe, environmentally friendly, low in maintenance or low in energy consumption as the present recovery system.
A number of devices have been used in the prior art to recover or utilize heat from the earth. One such device is disclosed by U. S. Pat. No. 4,042,012 of Aug. 16, 1977 which shows the use of a heat pump in combination with a heat exchanger and heat sink. The heat sink uses back-fill soil enhanced with water sub-particles to transfer heat (cold) to buried heat pipes having coiled portions. The heat pipes are formed with a closed fluid circuit which runs through a heat exchanger which also contains a second closed conduit which communicates to with a heat pump.
In construction of the heat sink, a hole is dug in the ground, and a bottom water impermeable sheet of synthetic polymer material is laid to conform to the hole walls. A coiled heat pipe is laid in the interior of the hole and the soil previously removed is mixed with water absorbent particles with the mixture then being used to bury the pipe. A roof is placed on the upper surface of the back-fill soil soaked water absorbent particles. The remainder of the back-fill is placed over the roof.
Another U. S. Pat. No. 4,142,576 of Mar. 6, 1977, discloses a heat pump which is similarly connected with a heat exchanger. A pump located outside the heat sink pumps fluid through submerged coils which are placed in a pit having a fluid impermeable plastic wall. The pit is filed with back-fill soil and water soaked absorbent particles in random dispersion. The pump re-circulates the water through the coils and the heat exchanger to effect a heat transfer to a heat pump having a refrigerant line which runs through the heat exchanger.
Still another U.S. Pat. No. 4,452,227 of Jun. 5, 1984, discloses a pit with a plastic liner filled with gravel and rock. Brine is pumped from the pit into a spray tray exposed to outdoor air and returned into the pit. The brine is pumped out of the pit into a heat exchanger.
Another U.S. Pat. No. 4,010,731 of Mar. 8, 1977, discloses a heat storage pit with a water impermeable liner tank made of plastic such as vinyl or polyethylene. A layer of sand a few inches thick is spread on the bottom of the tank to prevent puncturing. Protection for the sides of the tank may be in the form of a layer of sand or alternatively, plastic or plastic foam. The tank is filled with gravel and stones of uniform size to provide void spaces. Earth taken from the pit is used for filling the tank after it has been screened to develop water circulation voids. Water is then pumped through the aggregate and an insulating barrier which extends down from the top of the tank traps the hottest water in the central portion while the coolest water flows under the barrier into the side portion. In the central portion, the warmest water rises to the top where its heat comes into contact with the heat exchanger for the purpose of providing hot water and heat to the house.
Conventional heat pump systems utilize a compressor, fan, condensing and evaporating coils, control valves, refrigerant gases and air in order to provide a source of cooling in summer and a source of heating in fall, winter and spring. The condensing coil, fan compressor and controls are known as the `outdoor unit.` During operation, the outdoor unit either extracts heat from or releases heat to the ambient air depending upon the cycle used. This transfer of heat to or from the outdoor unit is accomplished by forcing air through the condenser coils by means of a fan.
While the conventional heat pump uses air as its primary transfer medium, the geothermal cell and its recovery system invention use a different approach. First, a thermal mass is achieved by the construction of the geothermal cell and filling it with clean water. Second, the recovery system utilizes a submersible pump, a submersible refrigerant compressor and a submersible coil to transfer heat to or from the geothermal cell. The water used in the geothermal cell is the primary transfer medium. Water within the geothermal cell has a specific heat of 1.0 btu/lb/F. and has a constant temperature (approximately 54.degree. F.) as opposed to air which has a low specific heat (approximately 0.24 btu/lb/F. at sea level) and wide temperature variations (-10.degree. F. to 11.degree. F.). This range falls within heat pump and heat exchanger maximum efficiency ranges.
Water, having superior heat transfer characteristics as compared to air (800 times greater specific volume and four times greater specific heat) makes the geothermal cell and recovery system far more efficient then the conventional heat pump system.